Apparatus for sterilizing articles



July 1 6 I B. A. BJORK 7 3,454,353

APPARATUS FOR STERILIZING ARTICLES Filed April 29, 1966 Sheet v of s ICONNECTION TO MANOMETER INVENTOR.

I ATT RNEY July 8, 1969 BJORK 3,454,353

APPARATUS FOR STERILIZING ARTICLES Sheet 2 of 3 Filed April 29, 1966 glllll C 05W TC EXPAN$|BLE AND CONTRACTIBLE BELLOWS A. ATTORNEY July 8, 1969 B. A. BJORK 3,454,353

APPARATUS FOR STERILIZING ARTICLES Filed April 29, 1966 Sheet 3 of s FIG. 5

' INVENTOR.

. M ATTORNEY United States Patent US. Cl. 214 16 Claims ABSTRACT OF THE DISCLOSURE A sterilizing system in which the presence of air in a sterilizing chamber is checked and verified during a work cycle or sterilizing program and utilizing such indication of air to modify the cycle or program. A small quantity of steam and any air that may be present is trapped in a place outside the sterilizing chamber after the system is evacuated, and a quantitative determination is made of the amount of air that may be present in the sterilizing chamber by checking and verifying the quantity of air present in the trapped steam by abstracting heat therefrom to convert the steam from gaseous to liquid phase. When the quantity of air in the trapped steam exceeds a predetermined quantity, the work cycle of the system is modified to remove from the system undesirable air present in the steam before the work cycle goes forward to sterilize articles in the sterilizing chamber.

My invention relates to apparatus for sterilizing articles in a closed chamber by alternately evacuating the chamber and injecting steam into the evacuated chamber to remove air from the chamber and the articles therein being sterilized.

In the field of medicine it is absolutely necessary to employ articles, such as instruments and bandages, for example, which are sterile and free from living germs or microorganisms. It has been proposed to sterilize articles by employing chemicals and by air or steam at elevated temperatures. Sterilizing articles by steam at elevated temperatures is considered most effective and lends itself to sterilizing methods which can be readily controlled. In order to make certain that articles treated in a sterilizing chamber or autoclave become sterile, it often has been necessary to subject the articles to steam at an elevated sterilizing temperature for a longer period of time than that necessary to destroy all living microorganisms at the elevated temperature at which sterilization is effected. It also has been the practice to reduce the length of time it takes to sterilize articles by employing steam which is at an elevated temperature higher than that actually necessary to destroy all living microorganisms. However, many articles requiring sterilization do not withstand steam at such higher elevated temperatures.

Air present in articles being sterilized adversely affects their sterilization. This is particularly true when textiles and woven fabrics like bandages, for example, in which air is present, are sterilized. When a relatively large package of woven fabric is placed in a sterilizing chamber and temperature sensitive members are distributed in different parts of the package, the temperature sensitive members indicate that, when steam at an elevated temperature is introduced into the chamber and the temperature of the chamber rises to a definite elevated temperature at which the package is sterilized and then remains at such definite elevated temperature, the temperature of the inner parts of the package and particularly those parts in which air is present, even in small amounts, lag behind the temperatures of the parts at or near the outer surface 3,454,353 Patented July 8, 1969 of the package and hence reach the sterilization temperature later than the parts at or near the outer surface thereof.

When all of the air present in a relatively large package of woven fabric is evacuated therefrom and steam at an elevated temperature is introduced under pressure into the sterilizing chamber, it has been found that the length of time it takes the inner parts of the package to reach the elevated sterilization temperature is not significantly longer than it takes the parts at or near the outer surface thereof to reach the sterilization tempeature. When the quantity of air in the sterilizing chamber is about 2 percent, for example, this quantity of air is not necessarily distributed uniformly throughout a package of woven fabric and throughout the sterilizing chamber but may be concentrated at a single point in the package which cannot be sterilized with certainty.

In view of the foregoing, it will be apparent that it is desirable to evacuate air rapidly and effectively from a sterilizing chamber and the articles therein and to check or verify quantitatively the quantity of air present in the sterilizing chamber. It has already been proposed to provide sterilizing systems having suitable controls for automatically sterilizing articles in a sterilizing chamber in accordance with a particular work cycle or sterilization program. The controls for such automatically operable sterilizing systems usually include instruments or lamps or both which function to indicate the phase or part of the work cycle or sterilizing program at a particular time during the operation of the sterilizing system. It also is desirable to check or verify the presence of air in the sterilizing chamber and articles therein during a work cycle of the sterilizing system. Further, it is also desirable to provide controls which not only check or verify the presence of air in the sterilizing chamber and articles therein but also can function to modify the operation of the sterilizing system when the quantity of air present in the sterilizing chamber exceeds a definite quantity. By way of example, such controls desirably may be of a type which can function to interrupt a particular work cycle or sterilization program.

It has been assumed above that the air present in a sterilization chamber and articles therein is that air normally encountered when the sterilization chamber is fluid-tight and effectively sealed from the surroundings. In practice, sterilizing equipment includes connections for piping, control valves, and gaskets for one or more closure members. Hence, a small leak may occur in the equipment through which air can flow into the sterilizing chamber when the chamber has been evacuated. In order to remove such air from the sterilizing chamber, it usually has been the practice to evacuate the chamber to produce a high vacuum therein, thereafter inject steam under pressure into the chamber, and then evacuate the chamber again. When this procedure is followed, it theoretically is possible to reduce the quantity of air in the sterilizing chamber to a relatively low value which will not adversely affect the sterilization of articles. Alternatively, the procedure indicated above makes it theoretically possible to reduce the quantity of air in the sterilizing chamber to such a relatively low value that sterilization of articles can be effected with steam at a moderately high temperature and with relatively short work cycles. However, when an extremely high vacuum is produced in the sterilization chamber, a large pressure differential exists between the pressure in the chambef and the pressure of the surrounding ambient air. Under these conditions, a relatively small leak in the sterilization chamber can adversely affect the sterilization of articles in the chamber. While a sterilization chamber having a volume of liters and a single leak therein of about 0.45 mm. can be evacuated by an ordinary vacuum pump to produce a vacuum of about 80 to 90 percent, such large quantities of air can pass into the chamber through a leak of this size to jeopardize the sterilization of articles in the chamber.

It is an important object of my invention, therefore, to provide an improvement for checking and verifying the presence of air in the sterilizing chamber and the material therein during a work cycle or sterilizing program of a sterilizing system.

Another object of the invention is to provide an improvement of this kind to indicate the presence of air in the sterilizing chamber and material therein and to utilize such indication to modify the work cycle or sterilizing program of the sterilizing system.

A further object of the invention is to provide an improvement of this kind in which a small quantity of gaseous fluid in the system, which includes steam as a constituent and in which any air that may be present, is trapped in a place at the exterior of the sterilizing chamber after the system is evacuated, and quantitatively determining the quantity of air that may be present in the sterilizing chamber by checking and verifying the quantity of air present in the trapped gaseous fluid by abstracting heat therefrom to convert the steam constituent from gaseous to liquid phase.

A still further object of the invention is to provide an improvement of this kind in which the work cycle of the sterilizing system is modified so that the system cannot continue to sterilize articles in the sterilizing chamber when the quantity of air in the trapped gaseous fluid exceeds a predetermined quantity.

A still further object of the invention is to provide an improvement of this kind in which the work cycle of the sterilizing system, when the quantity of air in the trapped gaseous fluid exceeds a predetermined quantity, is modified to remove from the system undesirable air present in the steam before the work cycle goes forward to sterilize articles in the sterilizing chamber.

In the preferred embodiment of my invention, the sterilizing system includes a space which is in communication with a sterilizing chamber, the chamber and space having steam therein and air that may be present. After producing a partial vacuum in the chamber and the space by evacuating the system, the space is closed and segregated from the chamber, and, while the space is under partial vacuum, to trap therein steam and air that may be present. Heat is abstracted from steam in the space to elfect condensation thereof. Liquid is conducted into the bottom of the space to form a body of the liquid therein. The liquid surface level of the body of liquid in the space rises therein responsive to condensation of steam and reaches a level depending upon the quantity of air in the space. Further, the sterilizing system desirably includes a control which normally is inactive and is rendered active responsive to a definite rise of the liquid level in the space depending upon a quantity of air therein which does not exceed a predetermined quantity.

Further objects and advantages of my invention will become apparent as the following description proceeds, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

In the drawings, FIG. 1 is a view diagrammatically illustrating a sterilizing system embodying my invention and operable in accordance with the principle thereof; FIG. 2 is an enlarged vertical sectional view, taken at line 22 of FIG. 3, of parts shown in FIG. 1 to illustrate details more clearly; FIG. 3 is a horizontal sectional view taken at line 3-3 of FIG. 2; FIG.. 4 is an enlarged fragmentary vertical sectional view of details shown in FIG. 2; and FIG. 5 is a view diagrammatically illustrating the electrical connections for controlling the operation of the sterilizing system illustrated in FIGS. 1 to 4, respectively,

In FIG, 1 of t e drawing, 1 have shown. my invention in connection with an autoclave or sterilizing Vessel 113 having thermally insulated Walls 120 defining a chamher or compartment 114 into which access may be had by a door or closure member 115 which is hinged to the front of the vessel and adapted to be locked in its closed position by a suitable latch mechanism (not shown) having an operating handle 116 which is rotatably mounted on the door.

The vessel 113 forms a part of a sterilizing system 112 having a base 109 provided with legs 108 for supporting the vessel on a suitable supporting surface or floor 110. The vessel 113 is provided with a steam jacket 117 which is of annular form and defines a part of the chamber 114. The jacket 117 is thermally insulated from the surroundings by the insulated walls and is connected in a line through which steam is supplied from a source of supply to the interior of the chamber 114.

As shown in FIG. 1, steam is supplied from a suitable source of supply to the bottom of the jacket 117 through a conduit 118 which may extend vertically upward through an opening 118 in the floor 110, and steam flows from the top of the jacket 117 through a conduit 119 to the rear closed end of the chamber 114. A deflector 121 is provided within the chamber 114 at the region steam is introduced therein through the conduit 119, such deflector functioning to deflect the steam to the upper part of the chamber and promote distribution thereof in the vessel 113. A valve 135 is provided in the conduit 118 for controlling the supply of steam to the jacket 117, and a magnetically-operated valve MV3 is provided in the conduit 119 for controlling the supply of steam into the chamber 114.

Condensate formed in the jacket 117 flows from the bottom thereof through a conduit 124 which extends downward through an opening 124' in the floor 110. A filter 122 and a condensate water discharge device 123 are connecte d in the conduit 124. The device 123 may be of any suitable type, such as a thermostatically controlled trap, for example, which controls flow of condensate in the conduit 124 responsive to rise and fall of condensate in the trap.

A vacuum pump VP of the water-ring type, which is driven by the motor VPM seen in FIG. 5, is connected to receive water under pressure from a suitable source of supply through a water supply line including a conduit 125 which extends upward through an opening 125 in the floor 110. A magnetically-operated valve MVl is connected in the conduit 125. The water supply line further includes a conduit 154 which receives water from the conduit 125, a device LV for checking the presence of air, which will be described hereinafter, and a conduit 155 which is connected to the inlet of the vacuum pump VP. From the vacuum pump VP water is discharged into a conduit 126 having an outlet 127 through which water flows to a drain opening 111 provided in the floor 110.

The bottom of the vessel 113 is provided with an outlet 128 having the upper end of conduit connected thereto. A valve 129 is interposed between the outlet 128 and the conduit 130. The valve 129 is manually movable between open and closed positions by a lever 131. The lower end of the conduit 130 is in communication with the outlet 127 which is located over the drain opening 111. The lever 131 and latch mechanism of the door 115 are interlocked in any suitable manner (not shown) to prevent opening of the door 115 when the discharge valve 129 is closed and the chamber 114 is under pressure or a partial vacuum.

The outlet 128 also is connected to the vacuum pump VP by a vacuum line which includes a conduit 132, magnetically-operated valve MV2, a conduit 148, the air checking device LV and conduit 155. A connection is provided from conduit 132 to the upper part of conduit 130 around the valve 129. This by-pass connection includes a conduit 133, a one-way valve 133 and a restricted passageway 133", whereby condensate collecting in conduit 132, when magnetically-operated valve MV2 is closed and the chamber 114 is at atmospheric pressure, can flow therefrom into conduit 130.

To the conduit 125 of the water supply line is connected a branch line which includes a conduit 134, a magnetically-operated valve MV4 and a restricted passageway 134" which is connected to the conduit 130. The water flowing into conduit 134 of the branch line is utilized to condense steam which flows into conduit 130 from the chamber 114.

To the upper part of the chamber 114 is connected one end of a conduit 137, the opposite end of which functions as an air inlet 146 in which a filter (not shown) desirably is provided. The fiow of air into the conduit 137 through the air inlet 146 is controlled by a magneticallyoperated valve MV5. Further, a valve 138 is provided in a bran-ch conduit from conduit 137 for connecting, for instance, a pressure gauge. A pulsator PS and constant pressure regulator PR are connected to conduit 137 and operable responsive to the pressure prevailing in the chamber 114. The pulsator PS, which is diagrammatically shown in FIGS. 1 and 5, comprises a bellows which expands and contracts responsive to changes in pressure in the chamber 114 and four microswitches which close and open in sequence depending upon the pressure prevailing in the chamber 114. The constant pressure regulator PR, which is connected by a member 107 to the conduit 137 and is responsive to change in pressure in the chamber 114, functions to control the magnetically-operated valve MV3 and regulate the supply of steam to the chamber 114.

In that part of conduit 132 closely adjacent to the outlet 128 of the chamber 114 are provided pressure detecting means 139a and temperature detecting means 13912. The pressure detecting means 139a is connected by a member 140a to a recording thermo-vacuum meter 141, and the temperature detecting means 139k is connected by a member 14% to a thermostat TE. A vacuum valve 142, which is connected by a member 142 to the exterior of the jacket 117, functions to prevent a partial vacuum being formed in the jacket. The valve 142 is connected by a member 142" to a pressure gauge 144 which indicates the pressure of the steam in the jacket 117.

FIG. 5 diagrammatically illustrates the electrical connections for operating the control devices shown in FIG. 1 and just described. The electrical connections include an automatic control member panel 145 for automatically operating the autoclave or sterilizing vessel 113 in accordance with definite programs which are adjustable, the control member panel being capable of starting and monitoring a particular work cycle or sterilizing program.

In accordance with my invention, I provide the air checking device LV to check and verify the quantity of air present in the chamber 114 in a particular phase of a work cycle or sterilizing program. As best shown in FIGS. 2 and 3, the air checking device LV comprises a casing 147 having a cylindrical top 147a and a fiat bottom 147b secured together in any suitable manner. The top 147a is provided with a vertical partition 152 which depends downward from the upper end thereof toward the bottom 147b and is spaced therefrom to form a gap or opening 151 between spaces 149 and 150 at opposite sides of the partition. The bottom 1471) is formed with an opening 153a which serves as a clean-out opening for the space 150 to remove foreign matter therefrom. The opening 153a is adapted to be closed by a plug 153b threadedly connected in the opening. The part of the bottom 14712 defining the space 149 is formed with an opening to which is connected the conduit 148 forming a part of the vacuum line in communication with the outlet 128 of the chamber 114, such vacuum line including the magnetically-operated valve MV2.

The upper end of the casing 147, at the side thereof defining the space 150, is formed with two openings to one of which is connected the conduit 154 forming a part of the water supply line, such line including the magnetically-operated valve MV1. The other opening in the upper end of the casing 147 is connected to the conduit 155 which forms a part of the water supply and vacuum lines and is connected to the inlet of the vacuum pump VP.

The top 147a of the casing 147 includes a space 157 which is defined by a vertically extending sleeve-like part 157a and is in communication with the space 149 through an opening 156 in a wall 161 separating the two spaces 157 and 149. A valve member 156a is provided in the opening 156 in the wall 161. The upper end of the sleevelike part 157a threadedly receives a cap or closure member 157b through an opening of which a hollow sleeve 158a extends vertically downward into the space 157. The hollow sleeve 158a, which is formed of electrical insulating material, carries a pin 158 whose upper end is connected to a conductor 159 which forms a part of the electrical connections shown in FIG. 5 and whose function will be described presently. To the casing 147 of air checking device LV is fixed a conductor 160 which, as will be described presently, is connected to a neutral or ground connection.

The sterilizing chamber 114 and spaces 149 and 157 of the device LV have a connection therebetween. This connection is formed by a part of the vacuum line and includes conduits 148 and 132 and the magnetically-operated valve MV2 therebetween. In a particular phase of a work cycle of the sterilizing system, the vacuum pump VP is driven by the motor VPM and the magneticallyoperated valves MV1 and MV2 are open, whereby the vacuum pump VP functions to evacuate the sterilizing system to produce a partial vacuum in the chamber 114 and the spaces 149 and 157. When evacuation of the system is started, the chamber 114 and spaces 149 and 157 have therein steam and any air that may be present. When the sterilizing system is being evacuated, the restricted passageway 151 functions to retain water in the space of the device LV and keep the spaces 149 and 157 depleted of water.

When the partial pressure produced in the chamber 114 and spaces 149 and 157 reaches a predetermined value, the vacuum pump motor VPM and magnetically-operated valves MV1 and MV2 are deenergized, whereby the vacuurn pump VP stops and the valves MV1 and MV2 close. When this occurs, evacuation of the sterilizing system is terminated and the connection between the chamber 114 and the spaces 149 and 157 is closed by the valve MV2. When the vacuum pump VP becomes inactive, the pressure above the liquid body in the space 150 increases to atmospheric pressure. Heat is abstracted from steam in the spaces 149 and 157 by the liquid in the space 150 to effect condensation of the steam. The condensation of steam in the spaces 149 and 157 enables liquid to flow from the space 150 through the restricted passageway 151 into the bottom of the space 149 to form a body of liquid in the spaces 149 and 157. The liquid surface level of the body of liquid in the spaces 149 and 157 rises therein responsive to condensation of steam trapped in the spaces and reaches a level depending upon the quantity of air in the spaces 149 and 157.

The liquid flowing into the spaces, 149 and 157 rises therein through an opening 156 in the wall 161. When the quantity of air, which forms an air blanket over the liquid in the spaces 149 and 157, does not exceed a predetermined quantity, the liquid surface level rises to a definite level which is sufficiently high for the lower end of the pin 158 to be immersed in the liquid and complete an electrical circuit which includes the conductors 159 and 160, the casing 147, pin 158 and the liquid body in the spaces 149 and 157. However, when the quantity of air forming the air blanket exceeds the predetermined quantity, the air prevents the liquid surface level from rising to the definite level so that a gap will be formed between the lower end of the pin 158 and the liquid in the space 7 157 and the electrical circuit, which includes the conductors 159 and 160, will not be completed.

The quantity of air which is trapped over the liquid body in the spaces 149 and 157 is quantitatively related to the quantity of air that is present in the chamber 114. When the quantity of air present in the chamber 114 and articles therein does not adversely affect or jeopardize sterilization of the articles, the quantity of air trapped over the liquid body in the spaces 149 and 157 will not exceed the predetermined quantity and the liquid surface level will rise sufiiciently in the spaces 149 and 157 for the lower end of the pin 158 to be immersed in the liquid. However, when the quantity of air in the chamber 114 and the articles therein does adversely affect and jeopardize the sterilization of the articles, the quantity of air trapped over the liquid body in the spaces 149 and 157 will exceed the predetermined quantity and the liquid surface level will be prevented from rising to the definite level and the electrical circuit, which includes the conductors 159 and 160, will not be completed.

The manner in which the air checking device LV functions can be employed simply to check or verify the presence of air in the sterilizing chamber 114 during a work cycle of the sterilizing system. Also, controls may be employed which cooperate with the air checking device LV and function to modify the operation of the sterilizing system when an excessive quantity of air is present in the sterilizing chamber 114.

The air checking device LV can be adjusted so that the circuit including the conductors 159 and 160 may be completed when a larger or smaller quantity of air is trapped over the liquid body in the spaces 149 and 157. This can be accomplished, for example, by increasing or decreasing the height of that part of space 157 which extends upward from the lower end of the pin 158 and by increasing and decreasing the length of the pin 158. The valve 156a in the wall 161 prevents liquid flowing too rapidly from the space 149 into the space 157 and avoids splashing of liquid in the space 157. Hence, the lower end of the pin 158 will be immersed in the liquid in the space 157 only when the liquid surface thereof is perfectly level and motionless.

In FIG. 4 I have illustrated another manner of preventing splashing of liquid in the space 157 when liquid flows therein from the space 149. In FIG. 4 a T-shaped tube 162 is threadedly connected in an opening 156 in the wall 161. Liquid passes upward through the vertical passage 162a of the T-shaped tube and is discharged horizontally from the opposing ends of the passage 162b.

The electrical connections for controlling the operation of the sterilizing system shown in FIGS. 1 to 4 are diagrammatically illustrated in FIG. 5. A main switch HS is provided to connect the sterilizing system to a source of electrical supply. When the switch HS is closed, a circuit is completed for the signal lamp S1. When closure member 115 is moved to its closed position, a switch DK is closed to complete a circuit for the signal lamp S2.

The operation of the sterilizing system can now be started by depressing the push button TK. This completes a circuit for a relay R1. This circuit is completed from contact 2 of switch DK through contacts 1 and 2 of relay R2, and contacts 1 and 2 of push button TK to one terminal of the coil of relay R1. The opposite terminal 10 of the coil of relay R1 is connected to a neutral or ground connection 35. The relay R1 is held in its energized or connected position by a holding circuit. The holding circuit is completed from contact 2 of switch DK through contact 1 of relay R2, contacts 1 and 3 of relay R1, point 31 of the program mechanism PV, and contacts 4 and 5 of relay R2 to the one terminal of the coil of relay R1. Point 32 in turn is connected to a coil of contractor K. This circuit is completed from point 32 of the program mechanism PV through terminals 1 and 3 of the coil of the contactor K to neutral connection 36, whereupon contactor K s n g z d and connects the vacuum pump motor VPM to a source of electrical supply. When the contactor K is energized, a circuit is also completed for the magnetically-operated valves MV1 and MV2 and a signal lamp S3. The circuits for the valves MV1 and MV2 are completed from the point 32 of the program mechanism PV through contacts 1 and 2 of contactor K and coils of valves MV1 and MV2 to the neutral or ground connection 36.

With the vacuum pump VP being driven by the motor VPM and water being supplied thereto through valve MV1, which now is open, the vacuum pump VP is rendered operable. Since the magnetically-operated valve MV2 is also open, the vacuum pump VP functions to evacuate the sterilizing chamber 114. The signal lamp S3, which is energized, indicates that the sterilizing chamber 114 is being evacuated.

The point 32 of the program mechanism PV is connected to point 22 thereof through a connection which includes point 23 and change-over switch CS2. When the vacuum pump VP has functioned to produce percent vacuum in the sterilizing system, a circuit is completed between the points 22 and 33 of the program mechanism PV. This circuit is completed from point 22 of the program mechanism PV through contact 4 of relay R3, microswitches i0 and 0.8 of pulsator PS, and through contact 9 of relay R3 to point 33. From point 33 a circuit is completed across the coil of relay R4 to the neutral or ground connection 35. When the coil of relay R4 is energized, the connection from point 31 to point 32 through change-over switch CS4 is shifted by the latter to point 30. When this occurs, a circuit is completed from point 30 to point 33. This circuit from point 30 includes contact 4 of relay R1, microswitch :0 of pulsator PS, and contact 9 of relay R3 to the point 33 Hence, a circuit is still completed from point 33 across the coil of the relay R4 to the neutral connection 35 to keep this relay energized. At the same time a circuit is completed from point 30 of the program mechanism PV to the point 32 thereof from which a circuit is completed for the coil of the contactor K and the coils of the magnetically-operated valves MV1 and MV2 in the manner explained above. The circuit from point 30 includes contact 4 of relay R1, microswitch 0.8 of pulsator PS, contact 4 of relay R3, point 22 of program mechanism PV, change-over switch CS2 to point 23 and from the latter to point 32.

When the vacuum pump VP has functioned to produce a vacuum of about 80 percent, vapor is introduced into the chamber 114 with the vacuum pump running and when the pressure has risen to about 40 percent vacuum in the sterilizing system, the microswitch -0.8 of the pulsator PS opens, thereby opening the connection just referred to from point 30 to point 32 of the program mechanism PV. When this occurs, the circuit for the coil of contactor K is broken and the vacuum pump motor VPM is disconnected from the source of electrical supply, thereby deenergizing and closing the valves MV1 and MV2.

When the sterilizing chamber 114 is at atmospheric pressure, the microswitch :0 of the pulsator PS opens. This in turn opens the circuit from point 30 to point 33, which has been described above, and this in turn deenergizes the coil of the relay R4 connected between the point 33 of the program mechanism PV and the neutral connection 35. When the coil of the relay R4 is deenergized, change-over switches CS1 to CS4 move back to the positions shown in FIG. 5. Under these conditions, a circuit is again completed from point 31 of program mechanism PV through change-over switch CS4 to point 32. From point 32 a circuit is again completed for the coil of the contactor K which, when energized, completes the circuits for the coils of the magnetically-operated valves MV1 and MV2 in the manner explained above, whereby the vacuum pump VP again functions to produce a vacuum in the sterilizing system.

Each time the vacuum pump VP has functioned to produce 80 percent vacuum in the sterilizing chamber 114, the magnetic valve MV3 is energized and opens the steam supply line 119 to supply steam to the sterilizing chamber 114. This circuit for the magnetically-operated valve MV3, starting from the point 30 of the program mechanism PV, includes point 19 which, through the changeover switch CS1, is connected to point 20 and through contacts 1 and 2 of the constant pressure regulator PR to the coil of valve MVSL At the same time the magnetically-operated valve MV4 is energized from the point 30 of the program mechanism PV by a connection which includes point 19. This opens the valve MV4 whereby water is discharged through the restricted passageway 134" into the conduit 130 to condense steam flowing therein through the outlet 128 of the sterilizing chamber 114. The circuits of the valves MV3 and MV4 are completed by connections from the coils thereof to the neutral or ground connection 36.

Each time an 80 percent vacuum is produced in the sterilizing chamber 114, a step relay SR is energized and advances one step. This is-accomplished by a connection from point 30 of the program mechanism PV to the coil of the step relay SR which includes contacts 4 and 6 of the relay R1 and terminal 3 of the step relay SR. This circuit for the step relay SR is completed by a connection from terminal 4 of the coil thereof to the neutral or ground connection 35. When the third step of the step relay SR occurs, the top cam of this relay moves to such a position that a connection is completed from the point 30 of the program mechanism PV to one terminal of the coil of relay R3 through terminals 7 and 8 of the step relay SR. The last-mentioned connection from point 30 to the coil of the relay R3 is maintained as long as the point 30 of the program mechanism PV is energized.

When a 40 percent vacuum is produced in the sterilization system, the vacuum pump motor VPM is deenergized and the vacuum pump VP stops. Further, the magnetically-operated valves MVl and MV2 are deenergized and closed. When this occurs, the air checking device LV functions in the manner explained above to check the presence of air in the sterilizing chamber 114. If the liquid flowing from the space 150 into the bottom of the space 149 rises in the spaces 149 and 157 to a level sufficiently high for the lower end of the pin 158 to contact the liquid, a circuit will be completed for the coil of the relay R3. This circuit from the neutral connection 36 includes the conductor 160, the casing 147 of the air checking device LV, the body of liquid therein, pin 158, conductor 159 and contacts 2 and 1 of the relay R3 to the terminal 10 of this relay.

When the coil of relay R3 is energized the circuit to the pin 158 is broken at the contacts 1 and 2 of the relay R3 and a holding circuit is completed for the coil of this relay. This holding circuit from the terminal 10 of the relay coil includes contacts 1 and 3 of relay R3 and terminals 10 of relays R2 and R1 to the neutral connection 35. When the coil of relay R3 is energized in the manner just explained, the circuit for the signal lamp S3 is broken at the contacts 4 and 5 of the relay R3. When the signal lamp S3 is extinguished, this indicates that the vacuum pump VP is not functioning to evacuate the sterilizing chamber 114.

Also, when the coil of the relay R3 is energized, a circuit will be completed for the signal lamp S6 which indicates a drying phase of the work cycle. This circuit includes the connection from the vacuum circuit to the signal lamp S6 through the contacts 4 and 6 of the relay R3. The relay R3 also functions to open the connection to a fault-indicating signal lamp S8, thereby locking the relay R3 in the program mechanism PV to the point 33 thereof by a connection Which includes contacts 7 and 9 of the relay R3. This last-mentioned connection shunts the microswitch '0 of the pulsator PS, whereby the pressure in the sterilizing chamber 114 can then increase above atmospheric pressure without being interrupted.

In the event the quantity of air in the spaces 149 and 157 of the air checking device LV exceeds the predetermined quantity and the liquid in the spaces 149 and 157 rises to a level which is below the lower end of the pin 158 and the latter is spaced from the liquid surface of the liquid body, as explained above, then the relay R3 will not 'be energized. In such case a circuit will be completed from point 30 of the program mechanism PV to the coil of relay R2 in the event a 20 percent vacuum prevails in the sterilizing chamber 114. From point 30 of the program mechanism PV this circuit includes contacts 7 and 8 of step relay SR, contacts 7 and 8 of the relay R3, microswitch 0.2 of the pulsator PS and contacts 9 and 7 of the relay R1 to the coil of the relay R2 which, from the terminal 10, is connected to the neutral point 35.

Energization of the coil of the relay R2 completes a circuit for the fault-indicating signal lamp S8. From the coil of the relay R2 this circuit includes the contacts 9 and 7 of the relay R2. At the same time that the faultindicating signal lamp S8 is energized the circuit for the coil of the relay R1 is opened at the contacts 4 and 5 of the relay R2. Also, a holding circuit is provided to keep the coil of the relay R2 energized through the contacts 1 and 3 of the relay R2. When the coil of the relay R1 is deenergized, the contacts 3 and 1 open the circuit to the point 31 of the program mechanism PV and the program mechanism is returned to its starting position.

The relay R2, which can be referred to as a fault coupling relay, can also interrupt the work cycle or program of the sterilizing system if it takes a longer time for the sterilizing system to reach atmospheric pressure than the length of time for which the change-over switch CS3 is adjusted to move from the position illustrated in FIG. 5 to its other position to connect the point 25 to the point 24 of the program mechanism PV. In such event the point 25 of the program mechanism PV is connected to the point 24 and a circuit is completed from the point 24 through contacts 9 and 7 of relay R1 to the coil of relay R2. In the event the time it takes for the sterilizing chamber 114 to reach the temperature for which the thermostat TB is set exceeds the time for which the change-over switch CS3 is adjusted to move from its position illustrated in FIG. 5 to its other position to connect the point 25 of the program mechanism PV to the point 26, the work cycle or program of the sterilizing system can be interrupted. In such case an electrical circuit is completed from the point 20 of the program mechanism PV, contacts 1 and 2 of the thermostat TE, points 25 and 24 of the program mechanism PV and contacts 9 and 7 of the relay R1.

In the event the sterilizing chamber 114 reaches the temperature for which the thermostat TB is set in a length of time which is longer than the time limit for which the change-over switch CS3 is adjusted to move from the position illustrated in FIG. 5 to its other position to connect the point 25 of the program mechanism PV to the point 26, the thermostat TE functions to open the circuit at its contacts 1 and 2 and at the same time a circuit is completed for the signal lamp S5 through the contacts 1 and 3 of the thermostat TE to indicate that steam is being supplied to the sterilizing chamber 114 and sterilization of articles therein is being effected. If the temperature at which sterilization of articles in the chamber 114 is being eifected falls below the temperature for which the thermostat TE is set, a circuit is again completed through the contacts 1 and 2 of the thermostat TE and the work cycle or program of the sterilization system is halted and stopped in the manner explained above.

However, if the work cycle or sterilization program is going forward in a normal manner, the constant pressure regulator PR, when the pressure in the sterilization chamher 114 reaches a predetermined normal value for which it is adjusted, will regulate the pressure in the chamber 114 by opening and closing magnetically-operated valve 1 1 MV3 to control the supply of steam to the sterilization chamber 114.

After sterilization of articles in the chamber 114 has been effected for a given length of time, the changeover switch CS1 of the program mechanism PV is shifted from its position connecting point 19 to point 20, which completes a. circuit for energizing the magnetically-operated valve MV3 to open the latter and supply steam to the chamber 114, to its position connecting point 19 to points 18, 22, 23 and 32, which completes circuits to vacuum pump motor VPM and magnetically-operated valves MV1 and MV2 to render the vacuum pump VP operable to evacuate the sterilizing system. When this occurs the circuits open for the signal lamps S4 and S5 which indicate that the constant pressure regulator PR and thermostat TE are not functioning and that sterilization of articles in the chamber 114 is not being effected. At the same time the circuit is completed for the signal lamp S6 which indicates that the work cycle is in its drying phase. The step rela-y SR remains in the same position to which it has been moved, as explained above, because the connection between the points 30 and 33 of the program mechanism PV remains intact.

The length of time that the sterilization system is evacuated is determined by the length of time the point 22 of the program mechanism PV is permitted to function to energize control devices which carry out the evacuating phase of the work cycle of the sterilization system. When the evacuating phase of the work cycle is concluded, the circuit from the point 22 of the program mechanism PV through the point 23 to the point 32 is interrupted by shifting the change-over switch CS2 from the position illustrated in FIG. 5 to its other position. When this occurs point 22 becomes effective to energize point 21 and complete a circuit for the magnetically-operated valve MVS. The valve MVS in its open position allows atmospheric air to enter the conduit 137 through the air inlet 146. Hence, the valve MVS functions as a pressure equalizing valve to enable the pressure in the sterilizing chamber 114 to increase to atmospheric pressure. When this occurs the circuit for the signal lamp S7 is completed which indicates that the work cycle or sterilization program has been completed. From point 21 of the program mechanism PV this circuit is completed through microswitch :0.0 of the pulsator PS to signal lamp S7. The door or closure member 115 now can be opened to remove the sterilized articles from the chamber 114. This opens the circuit for the relay R1 at the contacts 1 and 2 of the door switch DK. All the relays forming components of the electrical controls of the sterilizing system then return to their original positions.

The switch CS4 is activated by the relay R4. The switches CS1, CS2 and CS3 are motor driven and delayed. Relay R4 is activated during pulsation by the pulsator PS, microswitch 0.8, and is held by its own switch CS4 through switch PSifl. During sterilizing, this relay R4 is held by current through the switches 79 in relay R3 instead of switch PSiO. During pulsation, the relay R4 releases a coupling between an axle and the motor M in its deenergized position. The delays for the switches are: for CS3, 3 minutes; for CS1, 6 minutes; and for CS2, 12 minutes.

If for any reason the step relay SR does not stop in its starting position, a resetting circuit may be provided which, when the door 115 is moved to its open position, functions to advance the step relay SR to its starting position. Such resetting circuit may include a connection from the contacts 1 and 2 of the door switch DK and the contacts 1 and 2 of the relay R1 to the contacts 6, 5, 2 and 1 of the step relay SR.

Although a particular embodiment of the invention has been shown and described, it will be apparent to those skilled in the art that various modifications and changes may be made without departing from the spirit and scope of the invention, as pointed out in the following claims.

I claim:

1. Sterilizing apparatus comprising structure defining a chamber, a steam line for supplying steam from a source of supply to the chamber to sterilize material therein, first valve means in the steam line for controlling the supply of steam to the chamber, means defining a space, conduit means connecting the chamber and the lower part of the space, second valve means in said conduit means for opening and closing the connection between the chamber and the space, means for evacuating steam and any air that may be present from the chamber and the space and the connecting conduit means therebetween when the first valve means is closed and the second valve means is open, control means for starting and stopping the evacuating means, said space containing steam and the air that may be present when the evacuating means is stopped by the control means and the second valve means is closed, means for flowing liquid into the lower part of the space when the evacuating means is stopped by the control means and the space is under partial vacuum to trap in the space steam and the air that may be present, means for abstracting heat from the steam in the space to effect condensation thereof, means for flowing liquid into the lower part of the space to form therein a liquid body having a liquid surface level which rises responsive to condensation of steam trapped in the space and stops at a level depending upon the quantity of air in the space, an electrical circuit, means for completing the electrical circuit when the liquid surface level of the body of liquid in the space rises to a definite level, a first device operable to open and close the first valve means and a second device operable to open and close the second valve means and means operable, when the rise of the liquid surface level of the body of liquid in the space is insufiicient to complete the electrical circuit, to render the first device operable to close the first valve means and to render the second device operable to open the second valve means and to render the control means operable to start the evacuating means.

2. Sterilizing apparatus as set forth in claim 1 in which the means for completing the electrical circuit further includes first and second switch means, means responsive to stopping of the evacuating means by the control means for closing the first switch means, and means responsive to closing of the second valve means for closing the second switch means.

3. Sterilizing apparatus as set forth in claim 1 in which the definite level is located in the space to quantitatively relate the quantity of air in the space to a quantity of air in the chamber which is ineffective to jeopardize and adversely affect sterilization of material in the chamber and in which any level below the definite level is located in the space to quantitatively relate the quantity of air in the space to a quantity of air in the chamber which is effective to jeopardize and adversely affect sterilization of the material in the chamber.

4. Sterilizing apparatus as set forth in claim 1 in which the electrical circuit has at least one electrically conductive pin depending downward in the space at the upper part thereof and is completed when the liquid surface level of the body of liquid in the space rises to the definite level and the lower end of the pin contacts the liquid, the means defining the space including a horizontal partition to divide the space into upper and lower portions, the pin depending downward in the upper portion and having its lower end removed from and above the partition, the partition having an opening for liquid to fiow from the bottom portion of the space into the upper portion thereof, and means at the opening which functions to prevent splashing of liquid at the liquid surface level of the liquid in the upper portion of the space when liquid is being introduced therein.

5. Sterilizing apparatus as set forth in claim 1 in which the evacuating means comprises a vacuum line which is connected to the chamber and includes the conduit means and the space and a vessel, the vessel being disposed between the evacuating means and the space, the

lower parts of the space and the vessel being in communication with one another by passageway means, a liquid supply line for conducting liquid from a source of supply to the evacuating means, the liquid supply line including the vessel which is adapted to hold a body of liquid and into which liquid is introduced and from which liquid is withdrawn at the upper part thereof, the evacuating means functioning to produce a partial vacuum in the chamber and the space and the conduit means therebetween with the aid of liquid flowing thereto in the liquid supply line and also functioning to maintain the space depleted of liquid, and the means for flowing liquid into the lower part of the space comprising the vessel adapted to hold the body of liquid and the passageway means through which liquid from the vessel is adapted to flow into the lower part of the space responsive to the stopping of the evacuating means by the control means and rise in pressure above the body of liquid in the vessel to atmospheric pressure.

6. Sterilizing apparatus as set forth in claim in which the means for abstracting heat from the space to effect condensation of steam therein comprises the body of liquid adapted to be held in the vessel.

7. Sterilizing apparatus as set forth in claim 6 in which the body of liquid adapted to be held in the vessel is in heat conductive relation with the steam trapped in the space.

8. Sterilizing apparatus as set forth in claim 5 in which the evacuating means comprises a vacuum pump of the water-ring type and an electric motor for driving the pump, the vacuum pump receiving liquid through the liquid supply line, and the liquid in that part of the liquid supply line between the vessel and the vacuum pump flowing into the vessel responsive to stopping of the evacuating means by the control means.

9. Sterilizing apparatus as set forth in claim 8 in which comprises a casing divided into two compartments by a partition extending downward from the top thereof, the lower end of the partition being spaced from the bottom of the casing to provide a gap therebetween, one of the compartments serving as the vessel and the other of the compartments serving as the space, and the passageway means between the bottoms of the vessel and the space being defined by the gap between the lower end of the partition and the bottom of the casing.

10. Sterilizing apparatus comprising structure defining a chamber, a steam line for supplying steam from a source of supply to the chamber to sterilize material therein, first valve means in the steam line for controlling the supply of steam to the chamber, means defining a space, conduit means connecting the chamber and the lower part of the space, second valve means in said conduit means for opening and closing the connection between the chamber and the space, means for evacuating steam and any air that may be present from the chamber and the space and the connecting conduit means therebetween when the first valve means is closed and the second valve means is open, control means for starting and stopping the evacuating means, said space containing steam and the air that may be present when the evacuating means is stopped by the control means and the second valve means is closed, means for flowing liquid into the lower part of the space when the evacuating means is stopped by the control means and the space is under partial vacuum to trap in the space steam and the air that may be present, means for abstracting heat from the steam in the space to effect condensation thereof, means for flowing liquid into the lower part of the space to form therein a liquid body having a liquid surface level which rises responsive to condensation of steam trapped in the space and stops at a level depending upon the quantity of air in the space, an electrical circuit, means for completing the electrical circuit when the liquid surface level of the body of liquid in the space rises to a definite level, a first device operable to open and close the first valve means and a second device operable to open and close the second valve means, and means operable, when the rise of the liquid surface level of the body of liquid in the space is sufficient to complete the electrical circuit, to render the second device operable to close the second valve means and to render the control means operable to stop the evacuating means and to render the first device operable to open the first valve means to supply steam to the chamber to effect sterilization of material therein.

11. Sterilizing apparatus comprising structure defining a chamber, a steam line for supplying steam from a source of supply to the chamber to sterilize material therein, first valve means in the steam line for controlling the supply of steam to the chamber, means defining a space, conduit means connecting the chamber and the lower part of the space, second valve means in said conduit means for opening and closing the connection between the chamber and the space, means for evacuating steam and any air that may be present from the chamber and the space and the connecting conduit means therebetween when the first valve means is closed and the second valve means is open, control means for starting and stopping the evacuating means, said space containing steam and 'the air that may be present when the evacuating means is stopped by the control means and the second valve means is closed, means for flowing liquid into the lower part of the space when the evacuating means is stopped by the control means and the space is under partial vacuum to trap in the space steam and the air that may be present, means for abstracting heat from the steam in the space to effect condensation thereof, means for flowing liquid into the lower part of the space to form therein a liquid body having a liquid surface level which rises responsive to'condensation of steam trapped in the space and stops at a level depending upon the quantity of air in the space, an electrical circuit, means for completing the electrical circuit when the liquid surface level of the body of liquid in the space rises to a definite level, a first device operable to open and close the first valve means and a second device operable to open and close the second valve means, means operable, when the rise of the liquid surface level of the body of liquid in the space is insufficient to complete the electrical circuit, to render the first device operable to close the first valve means and to render the second device operable to open the second valve means and to render the control means operable to start the evacuating means, means operable, when the rise of the liquid surface level of the body of liquid in the space is suflicient to complete the electrical circuit, to render the second device operable to close the second valve means and to render the control means operable to stop the evacuating means and to render the first device operable to open the first valve means to supply steam to the chamber to effect sterilization of material therein, program mechanism for regulating the interval of time the second valve means is closed by the second device and the evacuating means is stopped by the control means and the first valve means is opened by the first device responsive to sufiicient rise of the liquid surface level of the body of liquid in the space to complete the electrical circuit to effect the principal sterilization of the material in the chamber to destroy all living micro-organisms in the materal during the principal sterilization phase of a work cycle, said program mechanism including preparatory means which functions in advance of and before the aforementioned principal sterilization phase of a work cycle is started to prepare the apparatus for the principal phase, the preparatory means being operable to expel air present in the chamber by rendering the first and second devices and the control means alternatively operable to effect evacuation of the chamber and to supply steam to the chamber, and means embodied in the program mechanism to render the preparatory means dependent upon a rise of the liquid surface level of the body of liquid in the space to at least the definite level to cause the program mechanism to start the principal sterilization phase of the material or to any level below the definite level to cause the program mechanism to stop functioning.

12. Sterilizing apparatus comprising structure defining a chamber, a steam line for supplying steam from a source of supply to the chamber to sterilize material therein, first valve means in the steam line for controlling the supply of steam to the chamber, means defining a space, conduit means connecting the chamber and the lower part of the space, second valve means in said conduit means for opening and closing the connection between the chamber and the space, means for evacuating steam and any air that may be present from the chamber and the space and the connecting conduit means therebetween when the first valve means is closed and the second valve means is open, control means for starting and stopping the evacuating means, said space containing steam and the air that may be present when the evacuating means is stopped by the control means and the second valve means is closed, means for flowing liquid into the lower part of the space when the evacuating means is stopped by the control means and the space is under partial vacuum to trap in the space steam and the air that may be present, means for abstracting heat from the steam in the space to effect condensation thereof, means for flowing liquid into the lower part of the space to form therein a liquid body having a liquid surface level which rises responsive to condensation of steam trapped in the space and stops at a level depending upon the quantity of air in the space, an electrical circuit having at least one electrically conductive pin depending downward in the space at the upper part thereof, means for completing the electrical circuit including the body of liquid in the space when the liquid surface level thereof rises to a definite level sufficiently high for the lower end of the pin to contact the liquid, the definite level being located in the space to quantitatively relate the quantity of air in the space to a quantity of air in the chamber which is ineffective to jeopardize and adversely affect sterilization of material in the chamber and in which any level below the definite level is located in the space to quantitatively relate the quantity of air in the space to a quantity of air in the chamber which is effective to jeopardize and adversely affect sterilization of the material in the chamber, a first device operable to open and close the first valve means and a second device operable to open and close the second valve means and means operable, when the rise of the liquid surface level of the body of liquid in the space is insufficient to complete the electrical circuit, to render the first device operable to close the first valve means and to render the second device operable to open the second valve means and to render the control means operable to start the evacuating means.

13. Sterilizing apparatus as set forth in claim 12 which includes a signal device, and means operable, when the rise of the liquid surface level of the body of liquid in the space is insufficient to complete the electrical circuit, to render the signal device operable.

14. Sterilizing apparatus comprising structure defining a chamber, a steam line for supplying steam from a source of supply to the chamber to sterilize material therein, first valve means in the steam line for controlling the supply of steam to the chamber, means defining a space, conduit means connecting the chamber and the lower part of the space, second valve means in said conduit means for opening and closing the connection between the chamber and the space, means for evacuating steam and any air that may be present from the chamber and the space and the connecting conduit means therebetween when the first valve means is closed and the second valve means is open, control means for starting and stopping the evacuating means, said space containing steam and the air that may be present when the evacuating means is stopped by the control means and the second valve means is closed, means for flowing liquid into the lower part of the space when the evacuating means is stopped by the control means and the space is under partial vacuum to trap in the space steam and the air that may be present, means for abstracting heat from the steam in the space to effect condensation thereof, means for flowing liquid into the lower part of the space to form therein a liquid body having a liquid surface level which rises responsive to condensation of steam trapped in the space and stops at a level depending upon the quantity of air in the space, an electrical circuit having at least one electrically conductive pin depending downward in the space at the upper part thereof, means for completing the electrical circuit including the body of liquid in the space when the liquid surface level thereof rises to a definite level sufficiently high for the lower end of the pin to contact the liquid, the definite level being located in the space to quantitatively relate the quantity of air in the space to a quantity of air in the chamber which is ineffective to jeopardize and adversely affect sterilization of material in the chamber and in which any level below the definite level is located in the space to quantitatively relate the quantity of air in the space to a quantity of air in the chamber which is effective to jeopardize and adversely affect sterilization of the material in the chamber, a first device operable to open and close the first valve means and a second device operable to open and close the second valve means, and means operable, when the rise of the liquid surface level of the body of liquid in the space is sufficient to complete the electrical circuit, to render the second device operable to close the second valve means and to render the control means operable to stop the evacuating means and to render the first device operable to open the first valve means to supply steam to the chamber to effect sterilization of material therein.

15. Sterilizing apparatus as set forth in claim 14 which includes a signal device, and means operable, when the rise of the liquid surface level of the body of liquid in the space is suflicient to complete the electrical circuit, to render the signal device operable.

l6. Sterilizing apparatus comprising structure defining a chamber, a steam line for supplying steam from a source of supply to the chamber to sterilize material therein, first valve means in the steam line for controlling the supply of steam to the chamber, means defining a space, conduit means connecting the chamber and the lower part of the space, second valve means in said conduit means for opening and closing the connection between the chamber and the space, means for evacuating steam and any air that may be present from the chamber and the space and the connecting conduit means therebetween when the first valve means is closed and the second valve means is open, control means for starting and stopping the evacuating means, said space containing steam and the air that may be present when the evacuating means is stopped by the control means and the second valve means is closed, means for flowing liquid into the lower part of the space when the evacuating means is stopped by the control means and the space is under partial vacuum to trap in the space steam and the air that may be present, means for abstracting heat from the steam in the space to effect condensation thereof, means for flowing liquid into the lower part of the space to form therein a liquid body having a liquid surface level which rises responsive to condensation of steam trapped in the space and stops at a level depending upon the quantity of air in the space, an electrical circuit having at least one electrically conductive pin depending downward in the space at the upper part thereof, means for completing the electrical circuit including the body of liquid in the space when the liquid surface level thereof rises to a definite level sufficiently high for the lower end of the pin to contact the liquid, the definite level being located in the space to quantitatively relate the quantity of air in the space to a quantity of air in the chamber which is ineffective to jeopardize and adversely affect sterilization of material in the chamber and in which any level below the definite level is located in the space to quantitatively relate the quantity of air in the space to a quantity of air in the chamber which is effective to jeopardize and adversely affect sterilization of the material in the chamber, a first device operable to open and close the first valve means and a second device operable to open and close the second valve means, means operable, when the rise of the liquid surface level of the body of liquid in the space is insuificient to complete the electrical circuit, to render the first device operable to close the first valve means and to render the second device operable to open the second valve means and to render the control means operable to start the evacuating means, means operable, when the rise of the liquid surface level of the body of liquid in the space is sufiicient to complete the electrical circuit, to render the second device operable to close the second valve means and to render the control means operable to stop the evacuating means and to render the first device operable to open the first valve means to supply steam to the chamber to effect sterilization of material therein, program mechanism for regulating the interval of time the second valve means is closed 'by the second device and the evacuating means is stopped by the control means and the first valve means is opened by the first device responsive to sufiicient rise of the liquid surface level of the body of liquid in the space to complete the electrical circuit to effect the principal sterilization of the material in the chamber to destroy all living micro-organisms in the material during the prinicpal sterilization phase of a work cycle, said program mechanism including preparatory means which functions in advance of and before the aforementioned principal sterilization phase of a work cycle is started to prepare the apparatus for the principal phase, the preparatory means being operable to expel air present in the chamber by rendering the first and second devices and the control means alternatively operable to effect evacuation of the chamber and to supply steam to the chamber, and means embodied in the program mechanism to render the preparatory means dependent upon a rise of the liquid surface level of the body of liquid in the space to at least the definite level to cause the program mechanism to start the principal sterilization phase of the material or to any level below the definite level to cause the program mechanism to stop functioning.

References Cited UNITED STATES PATENTS 7/ 1940 Walter 21-98 1/ 1959 Poitras 2l-94 XR 

